Electroless Palladium Gold Plating on Copper
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Solution Overview
Problem
In electroless palladium/gold plating processes, abnormal palladium precipitation occurs on compact-sized electrodes or narrow line/space copper wirings, leading to pinholes in the palladium plating film, which can cause failures in gold plating and degrade wire bonding properties.
Innovation Solution
A sulfur compound is adsorbed onto the copper surface to adjust its electric potential, allowing for selective formation of a palladium/gold plating film directly on copper without nickel intermediates, using a process that includes degreasing, copper oxide film removal, activation, surface electric potential adjustment, electroless palladium plating, and electroless gold plating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a nickel plating film of 3 μm or more is formed to prevent copper diffusion, then copper diffusion prevention is improved, but abnormal nickel precipitation between wirings occurs causing short circuits
Solution Approach 1:
The invention extracts the nickel plating layer from the plating structure, transitioning from a nickel/gold plating process to a direct copper/gold plating process. This eliminates the harmful nickel precipitation between wirings while maintaining copper diffusion prevention through the copper surface treatment and direct gold plating approach.
Solution Approach 2:
The invention changes the plating parameters by using a sulfur compound treatment on the copper surface to control the plating reaction. This surface treatment modifies the copper surface properties to enable controlled gold plating without nickel intermediate layer, preventing abnormal precipitation while maintaining protective function.
2Object-generated harmful factors
If the nickel plating film thickness is reduced to 1 μm or less to prevent nickel precipitation, then abnormal precipitation is reduced, but nickel local corrosion and pinhole formation occur
Solution Approach 1:
The invention removes the nickel plating layer entirely from the structure, replacing it with a direct copper surface treatment followed by gold plating. This eliminates both the nickel precipitation problem and the nickel corrosion/pinhole problem associated with thin nickel films.
Solution Approach 2:
The invention creates a composite surface structure consisting of copper base metal with sulfur compound treatment layer and gold plating layer. This composite structure provides both protection against copper diffusion and maintains film integrity without relying on nickel intermediate layers.
3Productivity
If L/S is narrowed to 10 μm or less for circuit densification, then circuit integration is improved, but abnormal nickel precipitation causes short circuits
Solution Approach 1:
The invention extracts the problematic nickel layer from the plating structure, enabling narrow L/S dimensions to be achieved without the risk of nickel precipitation causing short circuits. The direct copper surface treatment and gold plating approach maintains wiring integrity at dense configurations.
Solution Approach 2:
The invention changes the surface treatment parameters by applying sulfur compound treatment to copper surfaces, which controls the plating reaction characteristics. This enables reliable plating at narrow L/S dimensions by preventing abnormal precipitation while maintaining film quality.
4Ease of manufacture
If a palladium catalyst adsorption treatment is performed, then nickel plating catalysis is improved, but palladium and gold precipitate on abnormal nickel causing short circuits
Solution Approach 1:
The invention removes the nickel plating layer that serves as the substrate for abnormal palladium and gold precipitation. By eliminating the nickel layer entirely and using direct copper surface treatment with sulfur compounds followed by gold plating, the harmful precipitation on abnormal nickel is prevented.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach prevents abnormal palladium precipitation and pinhole formation, ensuring a reliable palladium/gold plating film on copper surfaces, even at narrow line/space dimensions, thereby enhancing the stability and integrity of electronic circuits.
Implementation Method 1
A sulfur compound is adsorbed onto the copper surface to adjust its electric potential
Implementation Method 2
forming a palladium plating film on copper and subsequently forming a gold plating film by electroless plating treatments
Data Source
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AI summary
It is an object of the present invention to provide an electroless palladium/gold plating process that can form a palladium/gold plating film selectively only on the copper without generating abnormal palladium precipitation even in a compact sized single electrode or a wiring with a narrow L/S. In order to solve the above-described problem, the electroless palladium/gold plating process comprises: a step (S4) of carrying out a copper surface electric potential adjusting treatment by immersing the insulating base material with a surface on which the copper has been disposed in a sulfur-containing aqueous solution containing one or more sulfur compounds selected from the group consisting of a thiosulfuric acid salt and a thiol; a step (S5) of carrying out an electroless palladium plating treatment on the insulating base material in which the surface electric potential of the copper has been adjusted to form a palladium plating film on the copper; and a step (S6) of carrying out an electroless gold plating treatment on the insulating base material in which the palladium plating film has been formed on the copper to form a gold plating film on the palladium plating film.